Real-IP middleware for Caddy

Middleware for restoring real ip information when running caddy behind a proxy. Will allow other middlewares to simply use r.RemoteAddr instead of decoding X-Forwarded-For themselves. Analogous to nginx's realip_module

Checks whitelist of authorized proxy servers so we don't arbitrarily trust headers from anybody.

The real IP module is useful in situations where you are running caddy behind a proxy server. In these situations, the actual client IP will be stored in an HTTP header, usually X-Forwarded-For. The problem this creates is that other directives that rely on the client IP address, like ipfilter or git, will not always work properly in these scenarios.

This middleware will seamlessly and securely read the real IP address from the appropriate header and replace the proxied IP in the request with the real one. The new IP wil lbe used in Caddy's log files and with other plugins.

Syntax

realip [cidr] {
    header name
    from   cidr [cidr... ]
    strict
}

name is the name of the header containing the actual IP address. Default is X-Forwarded-For.

cidr is the address range of expected proxy servers. As a security measure, IP headers are only accepted from known proxy servers. Must be a valid cidr block notation. This may be specified multiple times.

strict, if specified, will reject requests from unkown proxy IPs with a 403 status. If not specified, it will simply leave the original IP in place.

CIDR blocks

CIDR is a standard notation for specifying IP ranges. To allow a single IP, use /32 after the ip to specify no mask: 123.222.31.4/32. To allow all IPs (and accept an X-Forwarded-For header from anybody), use 0.0.0.0/0. Most cloud services should have their ip ranges published in this format somewhere.

Example

realip {
    from 1.2.3.4/32
    from 2.3.4.5/32
}

Presets

There is a few helpers supplied if you want to use Caddy behind cloud services. Simply specify the caddy snippet below in your caddyfile to activate it using a built-in IP list.

Provider	Alias	Caddyfile Snippet
Cloudflare	cloudflare	realip cloudflare
Google Cloud Platform	gcp	realip gcp
Rackspace Cloud	rackspace	realip rackspace

Additional presets would be welcome by pull request for other cloud providers.

Examples

Simple usage to read X-Forwarded-For from a few known IPs only:

realip {
    from 1.2.3.4/32
    from 2.3.4.5/32
}

Simple usage of preset and IP:

realip cloudflare 1.2.3.4/32

or

realip cloudflare {
    from 1.2.3.4/32
}

or

realip {
    from cloudflare
    from 1.2.3.4/32
}